1. Field of the Invention
The present invention relates to a magnetron sputtering apparatus for forming a metal film or an insulating film in fabricating a thin film semiconductor device.
2. Description of the Prior Art
Metal films of a thin film semiconductor device, in general, are formed by a magnetron sputtering apparatus. The magnetron sputtering apparatus induces ions of a reactive gas to impinge against a target and thus cause particles of the material from which the target is formed to be ejected therefrom and be deposited in a film over the surface of a wafer. The diameter of the target must be twice that of the wafer or greater and the peripheral portion of the target must be eroded more rapidly than the central portion of the same in order to form a film having a uniform thickness. When such a target larger than the wafer is used, most particles of the target fall on the surface of the wafer obliquely. Therefore, a drawback is encountered in that the particles of the target are unable to reach the bottom portions of a contact holes having a high aspect ratio and hence it is difficult to form a satisfactory film over the surface of the contact hole.
As shown in FIG. 6, a prior art magnetron sputtering apparatus 60 is provided with a particle interceptor 63 disposed between a wafer holder 61 for holding a wafer 71 thereon, and a target 62. The particle interceptor 63 is constructed by assembling a plurality of shading plates 64 in a grid so as to form through holes 65 through which particles of the target 62 travel. Most particles ejected from the surface 62a of the target 62 and traveling obliquely to the surface 71a of the wafer 71 held on the wafer holder 61 are arrested by the particle interceptor 63. Consequently, only the particles traveling in directions inclined at small angles to the normal to the surface 71a of the wafer 71 are able to pass through the through holes 65, to reach the surface 71a of the wafer 71 and to deposit in a satisfactory film, not shown, over the surface of the bottom portion of a contact hole, not shown, formed in the wafer 71.
However, problems arise in arresting the particles traveling obliquely to the surface 71a of the wafer 71 by the particle interceptor 63; most of the particles 64 traveling obliquely to the surface 71a of the wafer 71 deposit on the particle interceptor 63 as shown in FIG. 7. The particles 64 ejected from the peripheral portion 62a of the target 62 of a diameter 1.4 times the diameter of the wafer 71 or greater, in particular, are intercepted by the particle interceptor 63 and unable to reach the surface 71a of the wafer 71, and, consequently, the amount of the particles 64 of the target 62 that reach the surface 71a of the wafer 71 is reduced, reducing the availability of the target 62.
The particles 64 which traveled obliquely and which are arrested by the particle interceptor 63, accumulate in thick deposits 66 over the surface of the through holes 65 to narrow the same or, in the worst case, the through holes 65 are clogged with the deposits 66. Consequently, the particles 64 of the target 62 are unable to reach the surface 71a of the wafer 71 sufficiently and it is impossible to form a thick film efficiently over the surface 71a of the wafer
Furthermore, the thickness of a portion of the film formed in a region of the surface 71a of the wafer 71 covered by the shade of the particle interceptor 63 formed on the surface 71a by the orthogonal projection of the particle interceptor 63 is smaller than that of other portions of the film formed in regions of the surface 71a other than the region covered by the shade of the particle interceptor 63.